It's true we instinctively are judgemental on a subconscious level. Preference over fat or thin I think is an environmental indoctrination. In the west we are filtered with images that thin is beautiful fat is ugly (only now are we starting to change that negative bias in the media) but in certain African countries its been seen as big is beautiful (rich) and skinny (poor) and not desirable. Personally I'm not so judgemental about a person's weight but more about what they eat from a place of concern. That's goes for fat or skinny ppl because both sides can have bad or good diets. Normally you can tell if someone is healthy not just by the weight but by other factors, hair quality, eyes, skin etc these people I know on a subconcius level I'm more attracted too